Mechanism of automotive clearcoat damage by dragonfly eggs investigated by surface enhanced Raman scattering

摘要

Dragonflies are attracted by the reflection of sunlight on car surfaces and lay their eggs on the clearcoat resin. Considering that the surface can reach up to 93℃ and that during the egg hardening process (sclerotization) H_2O_2 is released, cysteine and cystine residues present in the egg protein can be oxidized to sulfinic and sulfonic acids. These are strong acids which, like acid rain, can hydrolyze the acrylic/melamine resin causing damage where the eggs were laid. Confocal Raman spectroscopy revealed that the spectra obtained from damaged and intact portions of the clearcoat were similar, in agreement with infrared absorption spectro- scopy data. These data demonstrate that the attack by eggs, H_2SO_4 and cysteine/H_2O_2 only promotes solubilization of resin through acid hydrolysis of the resin ester and amide moieties. Furthermore, surface enhanced Raman scattering (SERS) spectra obtained from dragonfly eggs and cysteine/H_2O_2 reaction products treated with a silver colloid were very similar, thus confirming the presence of sulfinic and sulfonic acids.